This invention relates to semiconductor devices; and, more particularly, to charge transfer devices capable of providing logic state inversion and bit regeneration.
One form of charge transfer devices, which has been termed "charge coupled devices," was first described in the copending U.S. patent application Ser. No. 11,541, filed Feb. 16, 1970, by W. S. Boyle and G. E. Smith, U.S. Pat. No. 3,858,232 and in the copending U.S. patent application Ser. No. 11,448, filed on the same date by D. Kahng and E. H. Nicollian now U.S. Pat. No. 3,651,349, issued Mar. 21, 1972. In these devices information is represented by electronic signals in the form of packets of charge carriers localized by induced potential energy minima in suitable storage media such as semiconductors, semi-insulating semiconductors, and insulators. Those copending applications specifically describe primarily a basic shift-register type of operation in which information is moved within the material by transferring the packets of charge sequentially from each potential well to the one next adjacent.
In another form of charge transfer devices, described in the copending U.S. application Ser. No. 11,447, filed Feb. 16, 1970, by C. N. Berglund and H. J. Boll, now U.S. Pat. No. 3,660,697, issued May 2, 1972 packets of charge carriers are gated sequentially from zone to zone along the surface of a semiconductive body which includes a bulk portion of one type semiconductivity and a plurality of spaced localized zones of the other type semiconductivity. In these devices each zone is operated as a potential well, the boundary of which is defined by the PN junction which defines the zone. This Berglund-Boll type of charge transfer apparatus is presently being referred to as the "bucket-brigade" type by those in the art; and so that designation will be used hereinbelow.
A problem early recognized in charge transfer devices is that a small fraction of the charge from each packet is left behind each time a packet is transferred from one potential well to another. Inasmuch as this charge loss results in signal degradation, some form of controlled charge regeneration and/or amplification must be provided if very long strings of information are to be so stored and processed.
And, of course, it is desirable to provide other modes of operation, such as, for example, complete sets of combinational logic functions. Perhaps the most basic of digital logic functions is "state inversion" (signal complementing) and "bit regeneration." Given these two basic functions, it is known that all other combinational logic functions, e.g., AND, OR, NAND, NOR, fan-in and fan-out, can be derived therefrom.